The orange line is the threshold voltage that the generator must match on the negative pin of the op-amp in order to sitch the trigger.
The blue line is the output of the circuit.
The green line is the input of the circuit.
The lower threshold (that is to say the minimum amount of voltage that the generator must match to make the generator switch up is 0 V, while the upper threshold is (in an ideal case) (2/3) of the generator max output.
